Google fonts; avoid too big transients when loading fonts

[simison]

Impacted plugin

Jetpack

What

Google Fonts module requests and caches all the fonts in one request, which might fail.

How

Part of #28118

Fonts API gets requested in backend in one big request, then cached, and returned styles are inlined at the site, both at the wp-admin and frontend of the site.

Admin side requests all the fonts (including weights 100—900 and styles) in one request, instead of requesting them gradually. At frontend fewer fonts are typically added, depending on how many were used to design the site.

When there are too many fonts, this results in over 10mb transients which fails. This happened when we started again adding more fonts (one, two) and request just grew too big. (See p1672355026291499-slack-jetpack)

Potential solutions:

• Split the request into multiple batches (good first remedy!).
• Add CSS minification to the API (pMz3w-g6E-p2s/#comment-104697), saves about ~20% kbs when caching
• Instead of loading from the fonts API in the backend, caching the response, and in-lining the styles, consider just requesting fonts API directly by client and let normal browser caching do the job.

[simison]

These APIs are deprecated longer ago already.